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Use of wastes derived from earthquakes for the production of concrete masonry partition wall blocks
Waste Management 31 (2011) 1859–1866
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Use of wastes derived from earthquakes for the production of concrete masonry partition wall blocks Zhao Xiao a,b, Tung-Chai Ling a, Shi-Cong Kou a, Qingyuan Wang b, Chi-Sun Poon a,⇑ a b
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Faculty of Architecture, Civil Engineering & Environment Engineering and Mechanics, Sichuan University, China
a r t i c l e
i n f o
Article history: Received 7 September 2010 Accepted 9 April 2011 Available online 12 May 2011 Keywords: Construction and demolition waste Crushed clay brick Recycled concrete aggregate Partition wall blocks Strength
a b s t r a c t Utilization of construction and demolition (C&D) wastes as recycled aggregates in the production of concrete and concrete products have attracted much attention in recent years. However, the presence of large quantities of crushed clay brick in some the C&D waste streams (e.g. waste derived collapsed masonry buildings after an earthquake) renders the recycled aggregates unsuitable for high grade use. One possibility is to make use of the low grade recycled aggregates for concrete block production. In this paper, we report the results of a comprehensive study to assess the feasibility of using crushed clay brick as coarse and fine aggregates in concrete masonry block production. The effects of the content of crushed coarse and fine clay brick aggregates (CBA) on the mechanical properties of non-structural concrete block were quantified. From the experimental test results, it was observed that incorporating the crushed clay brick aggregates had a significant influence on the properties of blocks. The hardened density and drying shrinkage of the block specimens decreased with an increase in CBA content. The use of CBA increased the water absorption of block specimens. The results suggested that the amount of crushed clay brick to be used in concrete masonry blocks should be controlled at less than 25% (coarse aggregate) and within 50–75% for fine aggregates. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The 12 May 2008 Sichuan earthquake, also known as Wenchuan earthquake, was one of the most destructive earthquakes in modern Chinese history causing significant economic impact and great loss of lives (Chen et al., 2010). It has been estimated that approximately 382 million tons of construction wastes derived mainly from collapsed buildings were generated (Xiao et al., 2009). The quantities of the building waste generated from Wenchuan earthquake far exceeded the annual production of building waste in China. In Sichuan, most of the residential and low-rise public buildings such as schools, hospitals and governmental offices were constructed with un-reinforced or unconfined masonry materials before or during the 1980s, and many of these building structures had practically no efficient seismic resistance (Zhao et al., 2009). As a result, they accounted for most of the full and partial collapses during the earthquake. The rubble mounds derived from 6.95 million collapsed buildings were mainly composed of waste concrete and large amount of waste masonry materials such as clay bricks (151.6 million tons).
⇑ Corresponding author. E-mail address: [email protected] (C.-S. Poon). 0956-053X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2011.04.010
Extensive studies have been undertaken over a long period by many researches to investigate the possibility of utilizing all kinds of waste to produce concrete blocks and brick products. For example, in Hong Kong the use of construction wastes such as recycled concrete aggregates and recycled crushed glass for manufacturing concrete block products has been successfully implemented and is gaining wider acceptance (Poon et al., 2002, 2009; Poon and Chan, 2006, 2007; Poon and Lam, 2008). Recently, a number of researchers have studied the possible use of crushed clay brick to produce concrete (Akhtaruzzaman and Hasnat, 1983; Khaloo, 1994; Padmini et al., 2001; Kibriya and Speare, 1996; Cachim, 2009). Akhtaruzzaman and Hasnat (1983) studied the use of crushed brick as a 100% replacement of coarse natural aggregates in concrete. It was found that the compressive strength of the brick concrete was lower than that of normal concrete, but the tensile strength of brick concrete was higher. Kibriya and Speare (1996) used three different types of brick aggregates to assess the impacts on long-term durability and strengths properties of the concrete. The results showed that the brick concrete had comparable compressive, tensile and flexural strengths to those of normal concrete but the modulus of elasticity was drastically reduced. An attempt was made by Corinaldesi (2009) and Corinaldesi et al. (2002) to use different kinds of recycled aggregate in preparing environmentally-friendly mortars. The results showed that the mechanical strength decreased when natural sand was
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substituted by the recycled aggregates (Corinaldesi and Moriconi, 2009). Nevertheless, the bond strength at the interface between the mortar and the brick aggregates seemed to be higher, mainly due to its improved rheological properties (Moriconi et al., 2003). Due to the potential problems of using crushed clay brick in concrete, the amount of crushed clay brick used has been restricted, which hinders the recycling of this masonry waste. On the other hand, some preliminary results have already shown that it is feasible to use crushed brick in non-structural paving block productions. Poon and Lam (2008) found that it was feasible to produce concrete blocks with 25% crushed clay brick incorporation that satisfied the compressive strength requirement for paving blocks to be used in trafficked areas prescribed by the Hong Kong government. Furthermore, the paving blocks with 50% crushed clay brick content satisfied the requirements specified by AS/NZS 4455 (1997) and Hong Kong government for pedestrian pavement applications. Schuur (2000) also proved that it is possible to use crushed clay brick derived from masonry waste to entirely replace sand for the production of calcium silicate products. However, there is currently limited data on the effect of higher percentages (>50%) of crushed clay brick on the production of concrete products. This paper presents a recent study at the Hong Kong Polytechnic University on the feasibility of using crushed clay brick as replacement for recycled concrete aggregates and natural river sand for the production of partition wall blocks. The main objective of this study was to develop appropriate technologies for the use of waste derived from demolished or collapsed masonry buildings as a contribution to manage the huge quantities of waste generated from the Wenchuan earthquake.
2. Experimental details 2.1. Materials 2.1.1. Ordinary Portland cement Ordinary Portland cement (OPC) was used as the cementing material to produce the block specimens. The OPC used was equivalent to BS 12 (1996) with a density of 3160 kg/m3 and was commercially available in Hong Kong.
2.1.2. Recycled concrete aggregate Recycled concrete aggregate (RCA) was obtained from a recycling facility located in Tuen Mun, Hong Kong. The recycling facility processed mainly concrete rubble sourced from demolition projects by crushing and sieving. The crushed concrete rubble was processed to pass through a mechanical sieving system to produce coarse and fine recycled aggregates with particle sizes of 10/5 mm (C-RCA) and less than 5 mm (F-RCA), respectively, according to the requirements of BS 812 (1995). The properties of RCA were tested according to BS 882 (1992) and the results are presented in Table 1. Fig. 1 shows the grading curves of the RCA.
2.1.3. Crushed clay brick The clay brick used in this study was solid red brick sourced from a local supplier, which was normally used for wall partition applications. The clay brick was crushed and sieved in the laboratory into different particle sizes (see Fig. 2). The crushed clay bricks were sorted into three groups according to their particle sizes: 10/ 5 mm (C-CBA) was used as coarse aggregate; whereas the <5 mm (F1-CBA) and <2.36 mm (F2-CBA) were used as fine aggregates. The physical properties of the coarse and fine clay brick aggregates were tested according to ASTM C128 and the results are listed in Table 1. The grading curves of these aggregates are shown in Fig. 1. 2.1.4. River sand River sand with a maximum size of 2.36 mm and a fineness modulus of 2.11 was used as the fine natural aggregates in this study. The sand was sourced from the Pearl River. The properties of the sand were tested according to BS 812 (1995) and the results are presented in Table 1. 2.2. Mix proportions of blocks A total of four series of blocks mixtures was designed in this study. The block specimens produced aimed to meet the requirements stipulated by BS 6073 (1981) (specification for partition wall block). All the mixtures were proportioned with a fixed total aggregate/cement ratio of 11.5, and 65% of the total aggregate was fine aggregates (<5 mm). In each of the mix series, five different mix proportions were prepared. In Series 1 and 2, in order to investigate the effect of using crushed clay brick as fine aggregates on concrete block properties, F1-CBA was used to replace sand at ratios of 25%, 50%, 75% and 100%. For the coarse aggregates, C-RCA/C-CBA ratios of 3 and 1 were used respectively in Series 1 and 2. For Series 3, the effect of using crushed clay brick as coarse aggregate was investigated with C-RCA was replaced by C-CBA at 25%, 50%, 75% and 100% by weight, while a sand/F1-CBA ratio of 1 was used as fine aggregates. In Series 4, the possibility to using a finer crushed clay brick aggregate in the fine aggregate system was investigated; F2-CBA was used to replace F-RCA by weight at ratios of 25%, 50%, 75% and 100%, and only C-RCA was used as the coarse aggregate. The details of the mix proportions listed in Tables 2 and 3. 2.3. Preparation of block specimens The block specimens was fabricated in the laboratory using a dry-mixed method that had been described in our previous research studies (Poon et al., 2002, 2009; Poon and Chan, 2006, 2007; Poon and Lam, 2008). Initially, cement, coarse and fine aggregates, were mixed in a pan mixer for approximately 3 min. After mixing, water was incrementally added to the mixtures until the desired moisture content for these dry mixtures was obtained. For fabrication of block specimens, only a small amount of water was required to prepare a cohesive mix but with zero slump
Table 1 Properties of recycled coarse and fine aggregates used in this study. Properties
Density-SSDa (kg/m3) Density-oven-dry (kg/m3) Water absorption (%) a
SSD – Saturated surface dry.
Coarse aggregate
Fine aggregate
5–10 mm
<5 mm
<2.36 mm
C-RCA
C-CBA
F-RCA
F1-CBA
F2-CBA
Sand
2366 2186 8.22
2036 1764 15.43
1932 1502 28.71
1839 1358 35.56
1609 1043 54.23
2620 – 0.88
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100 C-RCA C-CBA F-RCA F1-CBA F2-CBA BS882(10mm) BS882(5mm)
90
Percent passing (%)
80 70 60 50 40 30 20 10 0 0.15
0.3
0.6
1.18 2.36 Sieve size (mm)
5
10
15
Fig. 1. Grading curves of recycled coarse and fine aggregates.
Fig. 2. Photographs of the coarse and fine recycled aggregates.
Table 2 Descriptions of block mixtures. Series
Description
1
Coarse aggregate: fixed C-RCA/C-CBA ratio of 3 Fine aggregate: Sand, Replacement of sand with F1-CBA at 0%, 25%, 50%, 75% and 100% by weight
2
Coarse aggregate: fixed C-RCA/ C-CBA ratio of 1 Fine aggregate: Sand, Replacement of sand with F1-CBA at 0%, 25%, 50%, 75% and 100% by weight
3
Coarse aggregate: C-RCA, Replacement of C-RCA by C-CBA at 0%, 25%, 50%, 75% and 100% by weight Fine aggregate: fixed sand/F1-CBA ratio of 1
4
Coarse aggregate: C-RCA Fine aggregate: F-RCA, Replacement of F-RCA with F2-CBA at 0%, 25%, 50%, 75% and 100% by weight
(non-workability, which simulated the actual industrial production process of concrete blocks). Throughout the study, the amount of water required varied depending on the types of aggregate used. For example, in the case of using crushed clay brick (high water absorption capacity) in the mixture, the total amount of water needed was relatively higher (see Table 3). Steel moulds with internal dimensions of 200 mm in length, 100 mm in width, and 60 mm in depth were used to produce the block specimens. For each block, approximately 2.8 kg mixed materials were used. The materials were put into the mould in three layers of approximately equal depth. After filling each of the first two layers, a consistent manual compaction was applied using a hammer and a wooden stem. After the third layer was filled, a compression force at a rate of 600 kN/min was applied until the force reached 500 kN. Excess materials were then removed with a trowel. The fabricated block specimens were kept in the
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Table 3 Mix proportions of block mixtures. Notation
Cement
Coarse aggregate
Added watera
Fine aggregate <5 mm
a
<2.36 mm
C-RCA
C-CBA
F-RCA
F1-CBA
F2-CBA
Sand
Series 1 S1-0 S1-25 S1-50 S1-75 S1-100
1 1 1 1 1
3 3 3 3 3
1 1 1 1 1
– – – – –
0 1.875 3.750 5.625 7.500
– – – – –
7.500 5.625 3.750 1.875 0
0.16 0.26 0.34 0.45 0.47
Series 2 S2-0 S2-25 S2-50 S2-75 S2-100
1 1 1 1 1
2 2 2 2 2
2 2 2 2 2
– – – – –
0 1.875 3.750 5.625 7.500
– – – – –
7.500 5.625 3.750 1.875 0
0.22 0.30 0.37 0.44 0.58
Series 3 S3-0 S3-25 S3-50 S3-75 S3-100
1 1 1 1 1
4 3 2 1 0
0 1 2 3 4
– – – – –
3.750 3.750 3.750 3.750 3.750
– – – – –
3.750 3.750 3.750 3.750 3.750
0.33 0.35 0.37 0.39 0.40
Series 4 S4-0 S4-25 S4-50 S4-75 S4-100
1 1 1 1 1
4 4 4 4 4
– – – – –
7.500 5.625 3.750 1.875 0
– – – – –
0 1.875 3.750 5.625 7.500
– – – – –
0.22 0.24 0.43 0.41 0.49
Added water is the total mass of water added per cement weight.
steel moulds, covered by a plastic sheet and left at room temperature of 23 ± 3 °C and 75 ± 5 relative humidity (RH) for 24 h. The block specimens were then remoulded from the steel moulds and cured (covered by a hemp bag to maintain a RH of over 90%) at room temperature of 23 ± 3 °C until the date of testing at 7 and 28 days. 2.4. Test methods 2.4.1. Hardened density The density of block specimens was determined using a water displacement method as per BS 1881 Part 114 (1983) for hardened concrete. 2.4.2. Water absorption The cold water absorption values of the block specimens were determined in accordance with AS/NZS 4455 (1997). The water absorption was measured by immersing the oven dried block specimens in cold water at room temperature for 24 h. The values were expressed as a ratio of the mass of the absorbed water of an immersed block to the oven dried mass of the same specimen. 2.4.3. Compressive strength The compressive strength was determined by using a universal testing machine with a maximum capacity of 3000 kN. The loading rate of 450 kN/min was applied to the nominal area of the block specimen. Prior to the loading test, the block was soft capped with two pieces of plywood. Three samples were tested for each mix proportion. 2.4.4. Flexural strength The flexural strength of the block specimens was determined by a three-point bending test with a supporting span of 180 mm. For this test, test machine with a maximum load capacity of 50 kN was used and a displacement of 0.10 mm/min was set. Two samples were tested for each mix proportion.
2.4.5. Drying shrinkage The drying shrinkage of the block specimens was determined according to BS 6073 (1981). Many other researchers used this method and obtained reliable results (Poon et al., 2009; Gunduz, 2008). After 28 days of room temperature curing, the block specimens were immersed in water at room temperature for 24 h, and the initial length of the specimens were measured. After the initial reading, the specimens were conveyed to a drying chamber with a temperature of 23 °C and a relative humidity of 55% until further measurement at 1st, 3rd, 7th, 14th day. Each value represents the average of two measurements. 3. Results and discussion The hardened density, water absorption, compressive and flexural strengths as well as drying shrinkage test results of the block specimens are tabulated in Table 4. 3.1. Hardened density Fig. 3 shows the results of the hardened density of the block specimens. For Series 1 and 2, it shows that the hardened density of block specimens decreased with the increase of F-RCA content, reflecting the lower density of F-RCA as compared to river sand (see Table 1). The results of Series 3 indicate that the hardened density of the block specimens decreased with increasing C-CBA content due to the lower density of C-CBA. Therefore, as expected, when the F2-CBA was used to replace F-RCA, the density of the block specimens was also lower than those made with F-RCA. 3.2. Water absorption Fig. 4 shows the results of the water absorbed test. In all cases, block specimens containing recycled coarse and fine clay bricks aggregates had higher water absorption values when compared
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Density (kg/m3)
Water absorption (%)
Compressive strength (MPa)
Flexural strength (MPa)
7 days
28 days
7 days
Drying shrinkage (%)
28 days
Series 1 S1-0 S1-25 S1-50 S1-75 S1-100
2121 2112 2040 1971 1919
9.1 9.9 11.1 13.9 14.9
17.6 19.2 19.5 16.6 14.4
19.3 23.9 21.9 17.7 16.9
6.7 5.6 5.3 5.1 5.1
6.3 8.0 7.1 8.8 7.6
0.06 0.05 0.05 0.04 0.04
Series 2 S2-0 S2-25 S2-50 S2-75 S2-100
2104 2047 2013 1986 1967
9.5 10.8 12.5 13.5 16.3
15.4 14.5 17.1 14.8 9.3
16.0 17.6 19.2 18.9 14.9
5.7 5.8 5.3 5.7 3.5
6.3 7.5 7.8 7.9 7.2
0.05 0.04 0.05 0.04 0.03
Series 3 S3-0 S3-25 S3-50 S3-75 S3-100
2110 2040 2013 2008 1956
10.3 11.1 12.5 11.9 14.0
20.0 19.5 17.1 13.8 12.6
29.8 21.9 19.2 17.3 16.3
6.8 5.3 5.3 4.6 4.4
10.1 7.1 7.8 6.5 6.4
0.06 0.05 0.05 0.05 0.04
Series 4 S4-0 S4-25 S4-50 S4-75 S4-100
2138 2094 2047 2029 2017
13.9 14.4 14.7 14.9 15.5
11.2 16.5 18.1 15.3 11.2
12.6 16.3 21.0 17.2 15.3
– – – – –
6.0 9.5 9.4 10.7 10.1
0.07 0.05 0.04 0.04 0.03
2150 Series 1 Series 2
2100
Density (kg/m3)
Series 3 Series 4
2050
2000
1950
1900 0
25
50
75
100
Percentage of replacement Fig. 3. Hardened density of Series 1–4 block specimens.
to the blocks specimens prepared with recycled concrete aggregates or river sand. This is because crushed clay brick aggregates had higher water absorption capacity (see Table 1). The results of Series 1 and 2 indicate a systematic increase in water absorption values of the block specimens with the increase in F1-CBA content. For Series 3 and 4, as the C-RCA and F-RCA were entirely (100%) replaced by C-CBA and F2-CBA, the level of increase in water absorption was very high, recording an increase of 35.3% and 11.3%, respectively. 3.3. Compressive strength The 28-day compressive strength results of the block specimens are shown in Fig. 5. It can be seen that the compressive strength of the block specimens in Series 1, 2 and 4 was first increased and then decreased with the increase in the crushed clay brick content in the fine aggregate system. When the replacement level was in-
creased from 0% to 25% in Series 1 and from 0% to 50% in Series 2 and 4, the block specimens attained the highest compressive strength. Therefore, it can be concluded that for a given type of coarse aggregate, the use of a combination of different types in fine aggregates with different particle gradings would provide a better compressive strength probably due to the fact that the aggregates are well packed. Furthermore, the lower particle density of the finer CBA compared to that of the fine RCA and sand represented a higher volume of fine particles in the mixtures when RCA or sand was replaced by CBA. The finer CBA particles might have filled more voids and reduced the porosity and thus enhanced the mechanical properties. This finding is consistent with that of our previous study (Poon and Chan, 2007). Regarding the results of the compressive strength obtained in Series 3, the compressive strength gradually decreased with an increase in the C-CBA content. It was found that the compressive strength of block specimens prepared with 100% C-CBA was only
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17 16
Water absorption (%)
15 14 13 12 11
Series 1 Series 2
10
Series 3
9
Series 4
8 0
25
50
75
100
Percentage of replacement Fig. 4. Water absorption of Series 1–4 block specimens.
30
Compressive strength (MPa)
Series 1 Series 2 Series 3 Series 4
20
10 0
25
50
75
100
Percentage of replacement Fig. 5. Twenty-eight-day compressive strength of Series 1–4 block specimens.
approximately 54.5% of those of the prepared with pure C-RCA. Indeed this was expected because of the lower intrinsic strength of C-CBA when compared with C-RCA. Yang et al. (2011) carried out a study on concrete prepared with recycled concrete aggregate and crushed clay brick and observed a 5.7% loss in compressive strength when the natural aggregate was fully replaced by RCA. But loss of strength of approximately 11% and 20% were observed in the concrete prepared with 20% and 50% crushed clay brick ratios. 3.4. Flexural strength The results of the flexural strength of the block specimens are shown in Fig. 6. It is important to note that increase in crushed fine clay brick aggregate content effectively increased the flexural strength of the block specimens in Series 1, 2 and 4, and the highest flexural strengths was attained at the replacement level of 75%. The flexural strength of S1-75 and S2-75 block specimens was 40.3% and 24.5% higher than that of control samples (S1-0 and S2-0), respectively. In the case of using F2-CBA in Series 4, the increase in flexural strength of the block specimen was 79.6% at a replacement level of 75% as compared with the control sample (S4-0). As mentioned earlier, this was probably attributed to the better grading of the
combined use of different types of fine aggregates. In addition, since the flexural strength is mainly governed by the properties of the ITZ, and it been suggested that the inclusion of brick aggregates could allow the mortar to permeate the brick surface assuring a stronger physical interlock and ITZ (Moriconi et al., 2003). It is known that the flexural strength of the block specimens is highly dependant on the type and coarseness of aggregate content. In Series 3, as the replacement of C-RCA with C-CBA exceeded 25%, it resulted in a significant decrease in flexural strength. The decrease of flexural strength in the replacement level of 25%, 50%, 75% and 100% were 30.1%, 22.9%, 35.4% and 37.1% as compared with the control sample (S3-0), respectively. Similar findings were also reported by Corinaldesi and Moriconi (2009). 3.5. Drying shrinkage Fig. 7 shows the drying shrinkage values obtained of the specimens at 14 days were within the limit (60.06%) prescribed by BS 6073 (1981), except the S4-0 mix. The higher drying shrinkage value of S-4-0 (0.07%) was probably due to the mix contained only recycled concrete aggregate (without any crushed clay bricks). The drying shrinkage of the block specimens decreased with the increase in crushed coarse and fine clay brick aggregates
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Flexural strength (MPa)
11
9
7
Series 1
Series 2
Series 3
Series 4
5 0
25
50 Percentage of replacement
75
100
Fig. 6. Twenty-eight-day flexural strength of Series 1–4 block specimens.
0.080 Series 1
0.070
Series 2 Series 3
Drying shrinkage (%)
0.060
Series 4
0.050 0.040 0.030 0.020 0.010 0.000 0
25
50 Percentage of replacement
75
100
Fig. 7. Drying shrinkage of block specimens.
content and this is consistent with the results of a previous study (Bektas et al., 2009). The might be primarily due to the self-curing action of the brick aggregates in the block specimens. This beneficial effect of brick aggregates on reducing drying shrinkage was well documented in the literature (Corinaldesi and Moriconi, 2010). During the initial mixing, the crushed clay brick aggregates might have initially absorbed a relatively large amount of water (see Table 3) and this water was kept in the pores before it was released as the curing progressed. Therefore, the overall drying shrinkage was reduced owing to the presence of this internal moisture. 4. Conclusions The feasibility of using appropriate combination of low grade recycled aggregates for the production of partition wall blocks has been performed through laboratory scale experiments. Based on the laboratory results of this study, the following conclusions can be drawn: 1. The hardened density of block specimens decreased with the increase in crushed clay brick aggregates content, thus reflecting the lower density of crushed clay brick aggregates as compared to river sand or recycled concrete aggregates.
2. The water absorption of the block specimens increased with the increase of crushed clay brick aggregates content because the crushed clay brick aggregates had relatively higher water absorption capacity than that of the recycled concrete aggregates and river sand. 3. The use of a combination of different types of fine aggregates is likely to provide a better compressive strength. As for coarse aggregate replacement, the compressive strength was found to gradually decrease with an increase in the C-CBA content. 4. The highest flexural strength was attained when the replacement level of crushed fine clay aggregate reached the level of 75%. For coarse aggregate replacement, as the percentage of replacement level of C-RCA with C-CBA exceeded 25%, a significant decrease in flexural strength was observed. 5. The drying shrinkage of the block specimens decreased with the increase in the crushed coarse and fine clay brick aggregates contents. 6. The overall results demonstrate that it is feasible to use the waste clay brick derived from earthquakes as coarse and fine aggregates in the production of non-structural partition wall blocks. It is suggested that the percentage of coarse clay brick aggregates should be less than 25%, whereas as far as the percentage of fine clay brick aggregate is concerned, it should range between of 50% to 75%.
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Use of wastes derived from earthquakes for the production of concrete masonry partition wall blocks Zhao Xiao a,b, Tung-Chai Ling a, Shi-Cong Kou a, Qingyuan Wang b, Chi-Sun Poon a,⇑ a b
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Faculty of Architecture, Civil Engineering & Environment Engineering and Mechanics, Sichuan University, China
a r t i c l e
i n f o
Article history: Received 7 September 2010 Accepted 9 April 2011 Available online 12 May 2011 Keywords: Construction and demolition waste Crushed clay brick Recycled concrete aggregate Partition wall blocks Strength
a b s t r a c t Utilization of construction and demolition (C&D) wastes as recycled aggregates in the production of concrete and concrete products have attracted much attention in recent years. However, the presence of large quantities of crushed clay brick in some the C&D waste streams (e.g. waste derived collapsed masonry buildings after an earthquake) renders the recycled aggregates unsuitable for high grade use. One possibility is to make use of the low grade recycled aggregates for concrete block production. In this paper, we report the results of a comprehensive study to assess the feasibility of using crushed clay brick as coarse and fine aggregates in concrete masonry block production. The effects of the content of crushed coarse and fine clay brick aggregates (CBA) on the mechanical properties of non-structural concrete block were quantified. From the experimental test results, it was observed that incorporating the crushed clay brick aggregates had a significant influence on the properties of blocks. The hardened density and drying shrinkage of the block specimens decreased with an increase in CBA content. The use of CBA increased the water absorption of block specimens. The results suggested that the amount of crushed clay brick to be used in concrete masonry blocks should be controlled at less than 25% (coarse aggregate) and within 50–75% for fine aggregates. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The 12 May 2008 Sichuan earthquake, also known as Wenchuan earthquake, was one of the most destructive earthquakes in modern Chinese history causing significant economic impact and great loss of lives (Chen et al., 2010). It has been estimated that approximately 382 million tons of construction wastes derived mainly from collapsed buildings were generated (Xiao et al., 2009). The quantities of the building waste generated from Wenchuan earthquake far exceeded the annual production of building waste in China. In Sichuan, most of the residential and low-rise public buildings such as schools, hospitals and governmental offices were constructed with un-reinforced or unconfined masonry materials before or during the 1980s, and many of these building structures had practically no efficient seismic resistance (Zhao et al., 2009). As a result, they accounted for most of the full and partial collapses during the earthquake. The rubble mounds derived from 6.95 million collapsed buildings were mainly composed of waste concrete and large amount of waste masonry materials such as clay bricks (151.6 million tons).
⇑ Corresponding author. E-mail address: [email protected] (C.-S. Poon). 0956-053X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2011.04.010
Extensive studies have been undertaken over a long period by many researches to investigate the possibility of utilizing all kinds of waste to produce concrete blocks and brick products. For example, in Hong Kong the use of construction wastes such as recycled concrete aggregates and recycled crushed glass for manufacturing concrete block products has been successfully implemented and is gaining wider acceptance (Poon et al., 2002, 2009; Poon and Chan, 2006, 2007; Poon and Lam, 2008). Recently, a number of researchers have studied the possible use of crushed clay brick to produce concrete (Akhtaruzzaman and Hasnat, 1983; Khaloo, 1994; Padmini et al., 2001; Kibriya and Speare, 1996; Cachim, 2009). Akhtaruzzaman and Hasnat (1983) studied the use of crushed brick as a 100% replacement of coarse natural aggregates in concrete. It was found that the compressive strength of the brick concrete was lower than that of normal concrete, but the tensile strength of brick concrete was higher. Kibriya and Speare (1996) used three different types of brick aggregates to assess the impacts on long-term durability and strengths properties of the concrete. The results showed that the brick concrete had comparable compressive, tensile and flexural strengths to those of normal concrete but the modulus of elasticity was drastically reduced. An attempt was made by Corinaldesi (2009) and Corinaldesi et al. (2002) to use different kinds of recycled aggregate in preparing environmentally-friendly mortars. The results showed that the mechanical strength decreased when natural sand was
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substituted by the recycled aggregates (Corinaldesi and Moriconi, 2009). Nevertheless, the bond strength at the interface between the mortar and the brick aggregates seemed to be higher, mainly due to its improved rheological properties (Moriconi et al., 2003). Due to the potential problems of using crushed clay brick in concrete, the amount of crushed clay brick used has been restricted, which hinders the recycling of this masonry waste. On the other hand, some preliminary results have already shown that it is feasible to use crushed brick in non-structural paving block productions. Poon and Lam (2008) found that it was feasible to produce concrete blocks with 25% crushed clay brick incorporation that satisfied the compressive strength requirement for paving blocks to be used in trafficked areas prescribed by the Hong Kong government. Furthermore, the paving blocks with 50% crushed clay brick content satisfied the requirements specified by AS/NZS 4455 (1997) and Hong Kong government for pedestrian pavement applications. Schuur (2000) also proved that it is possible to use crushed clay brick derived from masonry waste to entirely replace sand for the production of calcium silicate products. However, there is currently limited data on the effect of higher percentages (>50%) of crushed clay brick on the production of concrete products. This paper presents a recent study at the Hong Kong Polytechnic University on the feasibility of using crushed clay brick as replacement for recycled concrete aggregates and natural river sand for the production of partition wall blocks. The main objective of this study was to develop appropriate technologies for the use of waste derived from demolished or collapsed masonry buildings as a contribution to manage the huge quantities of waste generated from the Wenchuan earthquake.
2. Experimental details 2.1. Materials 2.1.1. Ordinary Portland cement Ordinary Portland cement (OPC) was used as the cementing material to produce the block specimens. The OPC used was equivalent to BS 12 (1996) with a density of 3160 kg/m3 and was commercially available in Hong Kong.
2.1.2. Recycled concrete aggregate Recycled concrete aggregate (RCA) was obtained from a recycling facility located in Tuen Mun, Hong Kong. The recycling facility processed mainly concrete rubble sourced from demolition projects by crushing and sieving. The crushed concrete rubble was processed to pass through a mechanical sieving system to produce coarse and fine recycled aggregates with particle sizes of 10/5 mm (C-RCA) and less than 5 mm (F-RCA), respectively, according to the requirements of BS 812 (1995). The properties of RCA were tested according to BS 882 (1992) and the results are presented in Table 1. Fig. 1 shows the grading curves of the RCA.
2.1.3. Crushed clay brick The clay brick used in this study was solid red brick sourced from a local supplier, which was normally used for wall partition applications. The clay brick was crushed and sieved in the laboratory into different particle sizes (see Fig. 2). The crushed clay bricks were sorted into three groups according to their particle sizes: 10/ 5 mm (C-CBA) was used as coarse aggregate; whereas the <5 mm (F1-CBA) and <2.36 mm (F2-CBA) were used as fine aggregates. The physical properties of the coarse and fine clay brick aggregates were tested according to ASTM C128 and the results are listed in Table 1. The grading curves of these aggregates are shown in Fig. 1. 2.1.4. River sand River sand with a maximum size of 2.36 mm and a fineness modulus of 2.11 was used as the fine natural aggregates in this study. The sand was sourced from the Pearl River. The properties of the sand were tested according to BS 812 (1995) and the results are presented in Table 1. 2.2. Mix proportions of blocks A total of four series of blocks mixtures was designed in this study. The block specimens produced aimed to meet the requirements stipulated by BS 6073 (1981) (specification for partition wall block). All the mixtures were proportioned with a fixed total aggregate/cement ratio of 11.5, and 65% of the total aggregate was fine aggregates (<5 mm). In each of the mix series, five different mix proportions were prepared. In Series 1 and 2, in order to investigate the effect of using crushed clay brick as fine aggregates on concrete block properties, F1-CBA was used to replace sand at ratios of 25%, 50%, 75% and 100%. For the coarse aggregates, C-RCA/C-CBA ratios of 3 and 1 were used respectively in Series 1 and 2. For Series 3, the effect of using crushed clay brick as coarse aggregate was investigated with C-RCA was replaced by C-CBA at 25%, 50%, 75% and 100% by weight, while a sand/F1-CBA ratio of 1 was used as fine aggregates. In Series 4, the possibility to using a finer crushed clay brick aggregate in the fine aggregate system was investigated; F2-CBA was used to replace F-RCA by weight at ratios of 25%, 50%, 75% and 100%, and only C-RCA was used as the coarse aggregate. The details of the mix proportions listed in Tables 2 and 3. 2.3. Preparation of block specimens The block specimens was fabricated in the laboratory using a dry-mixed method that had been described in our previous research studies (Poon et al., 2002, 2009; Poon and Chan, 2006, 2007; Poon and Lam, 2008). Initially, cement, coarse and fine aggregates, were mixed in a pan mixer for approximately 3 min. After mixing, water was incrementally added to the mixtures until the desired moisture content for these dry mixtures was obtained. For fabrication of block specimens, only a small amount of water was required to prepare a cohesive mix but with zero slump
Table 1 Properties of recycled coarse and fine aggregates used in this study. Properties
Density-SSDa (kg/m3) Density-oven-dry (kg/m3) Water absorption (%) a
SSD – Saturated surface dry.
Coarse aggregate
Fine aggregate
5–10 mm
<5 mm
<2.36 mm
C-RCA
C-CBA
F-RCA
F1-CBA
F2-CBA
Sand
2366 2186 8.22
2036 1764 15.43
1932 1502 28.71
1839 1358 35.56
1609 1043 54.23
2620 – 0.88
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100 C-RCA C-CBA F-RCA F1-CBA F2-CBA BS882(10mm) BS882(5mm)
90
Percent passing (%)
80 70 60 50 40 30 20 10 0 0.15
0.3
0.6
1.18 2.36 Sieve size (mm)
5
10
15
Fig. 1. Grading curves of recycled coarse and fine aggregates.
Fig. 2. Photographs of the coarse and fine recycled aggregates.
Table 2 Descriptions of block mixtures. Series
Description
1
Coarse aggregate: fixed C-RCA/C-CBA ratio of 3 Fine aggregate: Sand, Replacement of sand with F1-CBA at 0%, 25%, 50%, 75% and 100% by weight
2
Coarse aggregate: fixed C-RCA/ C-CBA ratio of 1 Fine aggregate: Sand, Replacement of sand with F1-CBA at 0%, 25%, 50%, 75% and 100% by weight
3
Coarse aggregate: C-RCA, Replacement of C-RCA by C-CBA at 0%, 25%, 50%, 75% and 100% by weight Fine aggregate: fixed sand/F1-CBA ratio of 1
4
Coarse aggregate: C-RCA Fine aggregate: F-RCA, Replacement of F-RCA with F2-CBA at 0%, 25%, 50%, 75% and 100% by weight
(non-workability, which simulated the actual industrial production process of concrete blocks). Throughout the study, the amount of water required varied depending on the types of aggregate used. For example, in the case of using crushed clay brick (high water absorption capacity) in the mixture, the total amount of water needed was relatively higher (see Table 3). Steel moulds with internal dimensions of 200 mm in length, 100 mm in width, and 60 mm in depth were used to produce the block specimens. For each block, approximately 2.8 kg mixed materials were used. The materials were put into the mould in three layers of approximately equal depth. After filling each of the first two layers, a consistent manual compaction was applied using a hammer and a wooden stem. After the third layer was filled, a compression force at a rate of 600 kN/min was applied until the force reached 500 kN. Excess materials were then removed with a trowel. The fabricated block specimens were kept in the
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Table 3 Mix proportions of block mixtures. Notation
Cement
Coarse aggregate
Added watera
Fine aggregate <5 mm
a
<2.36 mm
C-RCA
C-CBA
F-RCA
F1-CBA
F2-CBA
Sand
Series 1 S1-0 S1-25 S1-50 S1-75 S1-100
1 1 1 1 1
3 3 3 3 3
1 1 1 1 1
– – – – –
0 1.875 3.750 5.625 7.500
– – – – –
7.500 5.625 3.750 1.875 0
0.16 0.26 0.34 0.45 0.47
Series 2 S2-0 S2-25 S2-50 S2-75 S2-100
1 1 1 1 1
2 2 2 2 2
2 2 2 2 2
– – – – –
0 1.875 3.750 5.625 7.500
– – – – –
7.500 5.625 3.750 1.875 0
0.22 0.30 0.37 0.44 0.58
Series 3 S3-0 S3-25 S3-50 S3-75 S3-100
1 1 1 1 1
4 3 2 1 0
0 1 2 3 4
– – – – –
3.750 3.750 3.750 3.750 3.750
– – – – –
3.750 3.750 3.750 3.750 3.750
0.33 0.35 0.37 0.39 0.40
Series 4 S4-0 S4-25 S4-50 S4-75 S4-100
1 1 1 1 1
4 4 4 4 4
– – – – –
7.500 5.625 3.750 1.875 0
– – – – –
0 1.875 3.750 5.625 7.500
– – – – –
0.22 0.24 0.43 0.41 0.49
Added water is the total mass of water added per cement weight.
steel moulds, covered by a plastic sheet and left at room temperature of 23 ± 3 °C and 75 ± 5 relative humidity (RH) for 24 h. The block specimens were then remoulded from the steel moulds and cured (covered by a hemp bag to maintain a RH of over 90%) at room temperature of 23 ± 3 °C until the date of testing at 7 and 28 days. 2.4. Test methods 2.4.1. Hardened density The density of block specimens was determined using a water displacement method as per BS 1881 Part 114 (1983) for hardened concrete. 2.4.2. Water absorption The cold water absorption values of the block specimens were determined in accordance with AS/NZS 4455 (1997). The water absorption was measured by immersing the oven dried block specimens in cold water at room temperature for 24 h. The values were expressed as a ratio of the mass of the absorbed water of an immersed block to the oven dried mass of the same specimen. 2.4.3. Compressive strength The compressive strength was determined by using a universal testing machine with a maximum capacity of 3000 kN. The loading rate of 450 kN/min was applied to the nominal area of the block specimen. Prior to the loading test, the block was soft capped with two pieces of plywood. Three samples were tested for each mix proportion. 2.4.4. Flexural strength The flexural strength of the block specimens was determined by a three-point bending test with a supporting span of 180 mm. For this test, test machine with a maximum load capacity of 50 kN was used and a displacement of 0.10 mm/min was set. Two samples were tested for each mix proportion.
2.4.5. Drying shrinkage The drying shrinkage of the block specimens was determined according to BS 6073 (1981). Many other researchers used this method and obtained reliable results (Poon et al., 2009; Gunduz, 2008). After 28 days of room temperature curing, the block specimens were immersed in water at room temperature for 24 h, and the initial length of the specimens were measured. After the initial reading, the specimens were conveyed to a drying chamber with a temperature of 23 °C and a relative humidity of 55% until further measurement at 1st, 3rd, 7th, 14th day. Each value represents the average of two measurements. 3. Results and discussion The hardened density, water absorption, compressive and flexural strengths as well as drying shrinkage test results of the block specimens are tabulated in Table 4. 3.1. Hardened density Fig. 3 shows the results of the hardened density of the block specimens. For Series 1 and 2, it shows that the hardened density of block specimens decreased with the increase of F-RCA content, reflecting the lower density of F-RCA as compared to river sand (see Table 1). The results of Series 3 indicate that the hardened density of the block specimens decreased with increasing C-CBA content due to the lower density of C-CBA. Therefore, as expected, when the F2-CBA was used to replace F-RCA, the density of the block specimens was also lower than those made with F-RCA. 3.2. Water absorption Fig. 4 shows the results of the water absorbed test. In all cases, block specimens containing recycled coarse and fine clay bricks aggregates had higher water absorption values when compared
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Density (kg/m3)
Water absorption (%)
Compressive strength (MPa)
Flexural strength (MPa)
7 days
28 days
7 days
Drying shrinkage (%)
28 days
Series 1 S1-0 S1-25 S1-50 S1-75 S1-100
2121 2112 2040 1971 1919
9.1 9.9 11.1 13.9 14.9
17.6 19.2 19.5 16.6 14.4
19.3 23.9 21.9 17.7 16.9
6.7 5.6 5.3 5.1 5.1
6.3 8.0 7.1 8.8 7.6
0.06 0.05 0.05 0.04 0.04
Series 2 S2-0 S2-25 S2-50 S2-75 S2-100
2104 2047 2013 1986 1967
9.5 10.8 12.5 13.5 16.3
15.4 14.5 17.1 14.8 9.3
16.0 17.6 19.2 18.9 14.9
5.7 5.8 5.3 5.7 3.5
6.3 7.5 7.8 7.9 7.2
0.05 0.04 0.05 0.04 0.03
Series 3 S3-0 S3-25 S3-50 S3-75 S3-100
2110 2040 2013 2008 1956
10.3 11.1 12.5 11.9 14.0
20.0 19.5 17.1 13.8 12.6
29.8 21.9 19.2 17.3 16.3
6.8 5.3 5.3 4.6 4.4
10.1 7.1 7.8 6.5 6.4
0.06 0.05 0.05 0.05 0.04
Series 4 S4-0 S4-25 S4-50 S4-75 S4-100
2138 2094 2047 2029 2017
13.9 14.4 14.7 14.9 15.5
11.2 16.5 18.1 15.3 11.2
12.6 16.3 21.0 17.2 15.3
– – – – –
6.0 9.5 9.4 10.7 10.1
0.07 0.05 0.04 0.04 0.03
2150 Series 1 Series 2
2100
Density (kg/m3)
Series 3 Series 4
2050
2000
1950
1900 0
25
50
75
100
Percentage of replacement Fig. 3. Hardened density of Series 1–4 block specimens.
to the blocks specimens prepared with recycled concrete aggregates or river sand. This is because crushed clay brick aggregates had higher water absorption capacity (see Table 1). The results of Series 1 and 2 indicate a systematic increase in water absorption values of the block specimens with the increase in F1-CBA content. For Series 3 and 4, as the C-RCA and F-RCA were entirely (100%) replaced by C-CBA and F2-CBA, the level of increase in water absorption was very high, recording an increase of 35.3% and 11.3%, respectively. 3.3. Compressive strength The 28-day compressive strength results of the block specimens are shown in Fig. 5. It can be seen that the compressive strength of the block specimens in Series 1, 2 and 4 was first increased and then decreased with the increase in the crushed clay brick content in the fine aggregate system. When the replacement level was in-
creased from 0% to 25% in Series 1 and from 0% to 50% in Series 2 and 4, the block specimens attained the highest compressive strength. Therefore, it can be concluded that for a given type of coarse aggregate, the use of a combination of different types in fine aggregates with different particle gradings would provide a better compressive strength probably due to the fact that the aggregates are well packed. Furthermore, the lower particle density of the finer CBA compared to that of the fine RCA and sand represented a higher volume of fine particles in the mixtures when RCA or sand was replaced by CBA. The finer CBA particles might have filled more voids and reduced the porosity and thus enhanced the mechanical properties. This finding is consistent with that of our previous study (Poon and Chan, 2007). Regarding the results of the compressive strength obtained in Series 3, the compressive strength gradually decreased with an increase in the C-CBA content. It was found that the compressive strength of block specimens prepared with 100% C-CBA was only
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17 16
Water absorption (%)
15 14 13 12 11
Series 1 Series 2
10
Series 3
9
Series 4
8 0
25
50
75
100
Percentage of replacement Fig. 4. Water absorption of Series 1–4 block specimens.
30
Compressive strength (MPa)
Series 1 Series 2 Series 3 Series 4
20
10 0
25
50
75
100
Percentage of replacement Fig. 5. Twenty-eight-day compressive strength of Series 1–4 block specimens.
approximately 54.5% of those of the prepared with pure C-RCA. Indeed this was expected because of the lower intrinsic strength of C-CBA when compared with C-RCA. Yang et al. (2011) carried out a study on concrete prepared with recycled concrete aggregate and crushed clay brick and observed a 5.7% loss in compressive strength when the natural aggregate was fully replaced by RCA. But loss of strength of approximately 11% and 20% were observed in the concrete prepared with 20% and 50% crushed clay brick ratios. 3.4. Flexural strength The results of the flexural strength of the block specimens are shown in Fig. 6. It is important to note that increase in crushed fine clay brick aggregate content effectively increased the flexural strength of the block specimens in Series 1, 2 and 4, and the highest flexural strengths was attained at the replacement level of 75%. The flexural strength of S1-75 and S2-75 block specimens was 40.3% and 24.5% higher than that of control samples (S1-0 and S2-0), respectively. In the case of using F2-CBA in Series 4, the increase in flexural strength of the block specimen was 79.6% at a replacement level of 75% as compared with the control sample (S4-0). As mentioned earlier, this was probably attributed to the better grading of the
combined use of different types of fine aggregates. In addition, since the flexural strength is mainly governed by the properties of the ITZ, and it been suggested that the inclusion of brick aggregates could allow the mortar to permeate the brick surface assuring a stronger physical interlock and ITZ (Moriconi et al., 2003). It is known that the flexural strength of the block specimens is highly dependant on the type and coarseness of aggregate content. In Series 3, as the replacement of C-RCA with C-CBA exceeded 25%, it resulted in a significant decrease in flexural strength. The decrease of flexural strength in the replacement level of 25%, 50%, 75% and 100% were 30.1%, 22.9%, 35.4% and 37.1% as compared with the control sample (S3-0), respectively. Similar findings were also reported by Corinaldesi and Moriconi (2009). 3.5. Drying shrinkage Fig. 7 shows the drying shrinkage values obtained of the specimens at 14 days were within the limit (60.06%) prescribed by BS 6073 (1981), except the S4-0 mix. The higher drying shrinkage value of S-4-0 (0.07%) was probably due to the mix contained only recycled concrete aggregate (without any crushed clay bricks). The drying shrinkage of the block specimens decreased with the increase in crushed coarse and fine clay brick aggregates
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Flexural strength (MPa)
11
9
7
Series 1
Series 2
Series 3
Series 4
5 0
25
50 Percentage of replacement
75
100
Fig. 6. Twenty-eight-day flexural strength of Series 1–4 block specimens.
0.080 Series 1
0.070
Series 2 Series 3
Drying shrinkage (%)
0.060
Series 4
0.050 0.040 0.030 0.020 0.010 0.000 0
25
50 Percentage of replacement
75
100
Fig. 7. Drying shrinkage of block specimens.
content and this is consistent with the results of a previous study (Bektas et al., 2009). The might be primarily due to the self-curing action of the brick aggregates in the block specimens. This beneficial effect of brick aggregates on reducing drying shrinkage was well documented in the literature (Corinaldesi and Moriconi, 2010). During the initial mixing, the crushed clay brick aggregates might have initially absorbed a relatively large amount of water (see Table 3) and this water was kept in the pores before it was released as the curing progressed. Therefore, the overall drying shrinkage was reduced owing to the presence of this internal moisture. 4. Conclusions The feasibility of using appropriate combination of low grade recycled aggregates for the production of partition wall blocks has been performed through laboratory scale experiments. Based on the laboratory results of this study, the following conclusions can be drawn: 1. The hardened density of block specimens decreased with the increase in crushed clay brick aggregates content, thus reflecting the lower density of crushed clay brick aggregates as compared to river sand or recycled concrete aggregates.
2. The water absorption of the block specimens increased with the increase of crushed clay brick aggregates content because the crushed clay brick aggregates had relatively higher water absorption capacity than that of the recycled concrete aggregates and river sand. 3. The use of a combination of different types of fine aggregates is likely to provide a better compressive strength. As for coarse aggregate replacement, the compressive strength was found to gradually decrease with an increase in the C-CBA content. 4. The highest flexural strength was attained when the replacement level of crushed fine clay aggregate reached the level of 75%. For coarse aggregate replacement, as the percentage of replacement level of C-RCA with C-CBA exceeded 25%, a significant decrease in flexural strength was observed. 5. The drying shrinkage of the block specimens decreased with the increase in the crushed coarse and fine clay brick aggregates contents. 6. The overall results demonstrate that it is feasible to use the waste clay brick derived from earthquakes as coarse and fine aggregates in the production of non-structural partition wall blocks. It is suggested that the percentage of coarse clay brick aggregates should be less than 25%, whereas as far as the percentage of fine clay brick aggregate is concerned, it should range between of 50% to 75%.
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